I was just thinking something like this myself.IMO instead of the difficulty coming from essentially overpowering the CPU and forcing the human player to rely increasingly on cheese(i.e.video gaming skills),it should come from becoming increasingly more realistic, forcing the human player to rely more and more on knowledge of the game of basketball rather than simply knowing what animations to exploit.
Basically it would break down to:
Pro= Your standard video gaming experience.
All Star= A balance between video gaming and realism.Would both teach and require a knowledge of the basic fundamentals of the real game of basketball.Good starting spot for those wanting to learn the mental side of the game.
Superstar= Mostly realistic with a touch of CPU assistance.For those that master the fundamentals but are not quite ready for full realism yet.Intermediate level knowledge and techniques taught and required.
HoF= The fully sim experience.For those that want their basketball as real as possible.Advanced level techniques introduced and required to perform well.
Online would probably stay reasonably similar(possibly tweaked slightly to account for online lag)...Park and My Team would be on Pro,JRC on All Star or Superstar, and Pro Am on HoF; PNO would have lobbies filtered by difficulty, MLO it would be 100% up to the players involved.